Intravenous amantadine is known to be effective for parkinsonian motor symptoms abruptly aggravated and for disabling motor symptoms from severe motor fluctuation and dyskinesia in patients with Parkinson's disease. The study investigators experienced several open label cases who were benefit from intravenous amantadine in their parkinsonian motor symptoms and freezing of gait as well. In addition, there is a pilot open label trial in parkinsonian patients with refractory freezing of gait which showed marked benefit in patients with Parkinson's disease, but not in patients with parkinson-plus syndromes.